1. Field of the Invention
The present invention relates to a display device, and more particularly to a display device which includes a display panel, a touch panel which is arranged on a surface of the display panel, and a front panel which is arranged on a surface of the touch panel.
2. Description of the Related Art
A liquid crystal display device (also referred to as “liquid crystal display module”) having a miniaturized TFT (Thin Film Transistor)-type liquid crystal display panel has been popularly used as a display part of portable equipment such as a mobile phone.
Recently, along with spreading of mobile equipment, a touch panel technique which supports a “user friendly” graphical user interface becomes important. In this respect, there has been known a liquid crystal display panel with a touch panel in which a touch panel substrate is mounted on a surface of the liquid crystal display panel and an operation corresponding to a menu is performed when a user touches a menu screen displayed on the liquid crystal display panel with his finger (see JP 2006-146895 A).
On the other hand, with respect to the above-mentioned liquid crystal display device, there has been known the structure in which on a viewer-side polarizer of a liquid crystal display panel, a front panel is fixed by way of an adhesive material having substantially the same refractive index as the polarizer (hereinafter referred to as “hybrid panel structure”). This hybrid panel structure, compared to the structure where a front panel is arranged on a viewer-side polarizer of a liquid crystal display panel with an air gap layer therebetween, has characteristics such as (1) being free from dusts (mixing of a small quantity of foreign substances), (2) reduction of thickness of the liquid crystal display panel, (3) favorable outdoor visibility, (4) high brightness and the like.
FIG. 7 is a cross-sectional view of an essential part for explaining a conventional liquid crystal display device having the hybrid panel structure with a touch panel.
In FIG. 7, symbol LCD indicates a liquid crystal display panel, symbol BL indicates a backlight, symbol 10 indicates a front panel, and symbol 100 indicates an electrostatic capacitance coupling type touch panel.
As the liquid crystal display panel LCD, for example, an IPS method liquid crystal display panel, a TN method liquid crystal display panel, a VA method liquid crystal display panel or the like is used. The liquid crystal display panel LCD is formed by laminating two substrates 1, 2 which are arranged to face each other in an opposed manner. Polarizers 3, 4 are provided to outer sides of two substrates respectively.
The liquid crystal display panel LCD and the touch panel 100 are adhered to each other by a first adhesive material 101 formed of a resin adhesive film or the like.
To an outer side of the touch panel 100, the front panel (also referred to as “front window”, “front surface protective plate”) 10 made of an acrylic resin or reinforced glass is adhered by a second adhesive material 102 formed of a resin adhesive film or the like.
The backlight BL is constituted of a resin mold frame (simply referred to as “mold” hereinafter) 11, a light guide plate 12 which is housed in the inside of the mold 11, a group of optical sheets 13 which is arranged on the light guide plate 12, a reflection sheet 14 which is arrange below the light guide plate 12, a light emitting diode (LD; not shown in the drawing) which is arranged on one side surface of the light guide plate 12 and functions as a light source, and a lower frame 60 which is arranged below the mold 11. Here, the group of optical sheets 13 is constituted of, for example, a lower diffusion sheet, two lens sheets and an upper diffusion sheet.
In the liquid crystal display device shown in FIG. 7, the front panel 10 has portions which overhang toward the outside from the touch panel 100 at four sides (showing only one side in FIG. 7) thereof, and lower surfaces of these portions are fixed to a casing 200 of portable equipment (for example, mobile phone) by a pressure sensitive adhesive double-coated tape 31, for example. Further, the first substrate 1 of the liquid crystal display panel LCD is fixed to the mold 11 by a pressure sensitive adhesive double-coated tape 30.
Further, the liquid crystal display panel LCD and the touch panel 100 are adhered to each other by the first adhesive material 101 formed of a resin adhesive film or the like, and the touch panel 100 and the front panel 10 are adhered to each other by the second adhesive material 102 formed of a resin adhesive film or the like.
Accordingly, an adhering portion between the touch panel 100 and the casing 200 or an adhering portion between the liquid crystal display panel LCD and the mold 11 is more liable to be peeled off compared to an adhering portion between the liquid crystal display panel LCD and the touch panel 100 or an adhering portion between the touch panel 100 and the front panel 10. Accordingly, when an impact is applied to the liquid crystal display device due to falling of the liquid crystal display device or the like, the touch panel 100 is peeled off from an adhering surface with the casing 200 or the liquid crystal display panel LCD is peeled off from an adhering surface with the mold 11, so that there exists a possibility that the liquid crystal display panel LCD comes out from the casing 200, or the backlight BL drops from the lower frame 60 and the liquid crystal display panel LCD comes out from the casing 200 together with the backlight BL.